This invention is in general related to analog to digital (i.e., A/D) converters and more particularly to successive approximation A/D converters.
A/D converters are used to convert an input analog voltage into an output digital (or binary) value. There are a number of different, known A/D conversion techniques, each having certain advantages which make it suitable for a particular application. In the successive approximation technique, the input, analog voltage is successively compared to some of a number of predefined, reference voltages using a comparator. The comparator has inverting and non-inverting voltage inputs, where one is to receive the input, analog voltage and the other is to successively receive some of the reference voltages. These reference voltages are typically evenly spaced between a lower voltage and an upper voltage (which are typically the voltages of the power supply and return nodes, respectively, used by the A/D converter), to define a number of non-overlapping voltage windows between the lower and upper voltages. Each voltage window is assigned a unique, digital value. A goal of the comparison process is to determine which voltage window contains the input, analog voltage, by performing a binary search. Each cycle of the search yields one bit, starting with the most significant bit, and with each cycle moves closer to the voltage window that contains the input voltage. The digital value assigned to this window is thus the output, digital value that represents the conversion of the input, analog voltage.